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Thu, 01 Dec 2022 14:07:15 +0200 Date: Thu, 1 Dec 2022 14:07:15 +0200 From: Andy Shevchenko To: Bartosz Golaszewski Cc: Kent Gibson , Linus Walleij , linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org, Bartosz Golaszewski Subject: Re: [PATCH v5 1/2] gpiolib: cdev: fix NULL-pointer dereferences Message-ID: References: <20221201083335.819190-1-brgl@bgdev.pl> <20221201083335.819190-2-brgl@bgdev.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221201083335.819190-2-brgl@bgdev.pl> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 01, 2022 at 09:33:34AM +0100, Bartosz Golaszewski wrote: > From: Bartosz Golaszewski > > There are several places where we can crash the kernel by requesting > lines, unbinding the GPIO device, then calling any of the system calls > relevant to the GPIO character device's annonymous file descriptors: > ioctl(), read(), poll(). > > While I observed it with the GPIO simulator, it will also happen for any > of the GPIO devices that can be hot-unplugged - for instance any HID GPIO > expander (e.g. CP2112). > > This affects both v1 and v2 uAPI. > > This fixes it partially by checking if gdev->chip is not NULL but it > doesn't entirely remedy the situation as we still have a race condition > in which another thread can remove the device after the check. > > Fixes: d7c51b47ac11 ("gpio: userspace ABI for reading/writing GPIO lines") > Fixes: 3c0d9c635ae2 ("gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL and GPIO_V2_LINE_GET_VALUES_IOCTL") > Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL") > Fixes: a54756cb24ea ("gpiolib: cdev: support GPIO_V2_LINE_SET_CONFIG_IOCTL") > Fixes: 7b8e00d98168 ("gpiolib: cdev: support GPIO_V2_LINE_SET_VALUES_IOCTL") > Signed-off-by: Bartosz Golaszewski > Reviewed-by: Andy Shevchenko > --- > drivers/gpio/gpiolib-cdev.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c > index 0cb6b468f364..911d91668903 100644 > --- a/drivers/gpio/gpiolib-cdev.c > +++ b/drivers/gpio/gpiolib-cdev.c > @@ -201,6 +201,9 @@ static long linehandle_ioctl(struct file *file, unsigned int cmd, > unsigned int i; > int ret; > > + if (!lh->gdev->chip) > + return -ENODEV; > + > switch (cmd) { > case GPIOHANDLE_GET_LINE_VALUES_IOCTL: > /* NOTE: It's okay to read values of output lines */ > @@ -1384,6 +1387,9 @@ static long linereq_ioctl(struct file *file, unsigned int cmd, > struct linereq *lr = file->private_data; > void __user *ip = (void __user *)arg; > > + if (!lr->gdev->chip) > + return -ENODEV; > + > switch (cmd) { > case GPIO_V2_LINE_GET_VALUES_IOCTL: > return linereq_get_values(lr, ip); > @@ -1410,6 +1416,9 @@ static __poll_t linereq_poll(struct file *file, > struct linereq *lr = file->private_data; > __poll_t events = 0; > > + if (!lr->gdev->chip) > + return 0; EPOLLHUP ? > poll_wait(file, &lr->wait, wait); > > if (!kfifo_is_empty_spinlocked_noirqsave(&lr->events, > @@ -1429,6 +1438,9 @@ static ssize_t linereq_read(struct file *file, > ssize_t bytes_read = 0; > int ret; > > + if (!lr->gdev->chip) > + return -ENODEV; > + > if (count < sizeof(le)) > return -EINVAL; > > @@ -1716,6 +1728,9 @@ static __poll_t lineevent_poll(struct file *file, > struct lineevent_state *le = file->private_data; > __poll_t events = 0; > > + if (!le->gdev->chip) > + return 0; > + > poll_wait(file, &le->wait, wait); > > if (!kfifo_is_empty_spinlocked_noirqsave(&le->events, &le->wait.lock)) > @@ -1740,6 +1755,9 @@ static ssize_t lineevent_read(struct file *file, > ssize_t ge_size; > int ret; > > + if (!le->gdev->chip) > + return -ENODEV; > + > /* > * When compatible system call is being used the struct gpioevent_data, > * in case of at least ia32, has different size due to the alignment > @@ -1821,6 +1839,9 @@ static long lineevent_ioctl(struct file *file, unsigned int cmd, > void __user *ip = (void __user *)arg; > struct gpiohandle_data ghd; > > + if (!le->gdev->chip) > + return -ENODEV; > + > /* > * We can get the value for an event line but not set it, > * because it is input by definition. > @@ -2407,6 +2428,9 @@ static __poll_t lineinfo_watch_poll(struct file *file, > struct gpio_chardev_data *cdev = file->private_data; > __poll_t events = 0; > > + if (!cdev->gdev->chip) > + return 0; > + > poll_wait(file, &cdev->wait, pollt); > > if (!kfifo_is_empty_spinlocked_noirqsave(&cdev->events, > @@ -2425,6 +2449,9 @@ static ssize_t lineinfo_watch_read(struct file *file, char __user *buf, > int ret; > size_t event_size; > > + if (!cdev->gdev->chip) > + return -ENODEV; > + > #ifndef CONFIG_GPIO_CDEV_V1 > event_size = sizeof(struct gpio_v2_line_info_changed); > if (count < event_size) > -- > 2.37.2 > -- With Best Regards, Andy Shevchenko